1. Field of the Invention
This invention relates to the preparation of sulfonic acid salts.
2. Description of the Prior Art
The conversion of the product from the sulfonation of olefins into sulfonic acid salts having utility as detergent components is described in numerous patents including U.S. Pat. Nos. 2,061,617; 2,187,244; 3,332,880; 3,488,384; 3,496,225 and 3,642,881. Generally speaking, the conversion has been accomplished in the prior art by reacting the crude sulfonated olefins (acid mix) at elevated temperature with an aqueous solution of a strong base such as NaOH to provide sulfonic acid salts whose cations correspond to those in the base. There is thus obtained a sulfonic acid salt product which may be treated several ways to produce a useful detergent composition. Typically, the amount of water supplied in solution with the base used is adjusted to provide a sulfonic acid salt solution containing 30-40 percent by weight of the salt and which is useful for blending with various detergent active and adjuvant materials such as amine oxides, alkanol amides, alcohol ethoxy sulfates, etc. to produce light duty liquid concentrates useful for dishwashing purposes.
The foregoing conversion of acid mix from olefin sulfonation with base is frequently called hydrolysis or saponification since it usually involves the more or less concurrent conversion of sulfonic acids to salts and the hydrolysis of esters or ester-like materials, including sultones. Generally, the reaction is required to be performed under rather severe conditions with strong reagents (e.g. 150.degree. C. for 1 hour under autogenous pressure using aqueous NaOH) because of the inherent slowness of the hydrolysis of some of the sultone or ester-like materials. Usually a considerable percentage of water is required to be used in the conversion system because aqueous solutions of sulfonic acid salts more concentrated than about 40 percent sulfonic acid salts have a pronounced tendency toward gelling. Such gelling interferes with the conversion as well as with the subsequent use of the product. Unfortunately, the 35-40 percent sulfonic acid salt solutions involve substantial shipping and storage costs because of the water content as well as of the cation material present. This necessitates the existence of numerous small scale sulfonation plants supplying limited geographical areas preventing cost savings that could otherwise be obtained through large scale plant operations. It would be advantageous to have a stable anhydrous composition which can be shipped at lower cost per pound of sulfonate salts or precursors contained therein.
Much of the prior art emphasis in connection with the sulfonation of olefins to produce olefin sulfonate salts is centered about the treatment of SO.sub.3 sulfonation effluent acid-mix containing mainly free sulfonic acids and about 30-40 percent sultones. U.S. Pat. No. 3,332,880 describes sulfonate salt mixtures containing about 30-70 percent alkene sulfonic acid salts, about 20-70 percent hydroxy alkyl sulfonic acid salts and about 2-15 percent disulfonate salts. Olefin sulfonation procedures using uncomplexed SO.sub.3 are frequently preferred since these procedures are considered to be conducive to the formation of 3- or 4-hydroxy alkane sulfonic acid salts rather than 2-hydroxy alkane sulfonic acid salts.
Olefin sulfonation processes are known to co-produce disulfonates and higher order polysulfonates in appreciable percentages such as 15 percent or higher. Some authorities consider that disulfonates are undesired as detergent components because of their highly polar nature. Usually one can control the production of disulfonates to some extent by controlling the mol ratio of SO.sub.3 to olefin used in the sulfonation step. Where the SO.sub.3 :olefin ratio is about 1:1 or less, the amount of disulfonates is generally less than it is with higher SO.sub.3 :olefin ratios. On the other hand, SO.sub.3 :olefin ratios lower than about 1:1 result in poor utilization of the olefins due to the failure of some olefin molecules to be sulfonated. Generally, the prior art prefers an SO.sub.3 :olefin mol ratio of from about 1:1 to about 1.2:1, typically about 1.1:1 as a reasonable compromise between disulfonates and "free oil" content (unsulfonated olefins).